Members of the Senate Finance Committee pounced on a Monday report from the insurance lobby group America’s Health Insurance Plans, which concluded their health bill would actually increase the amount consumers pay for insurance premiums.

“The insurance industry ought to be ashamed at this report,” Sen. John Kerry (D., Mass.) told the panel. “It’s a powerful argument for why we ought to have a public plan.”

Kerry pivoted to say that he’ll push to include a new public health insurance plan in the bill once it moves to the floor. The current bill lacks such a plan and instead calls for the government to help set up nonprofit cooperatives designed to increase competition with private insurers.

The backlash from Democrats underscored the growing tensions between lawmakers and the insurance industry. Insurers had pledged to cooperate with the health overhaul and not sink it, like they did in the failed 1993-1994 attempt to fix the health system. But they’re frustrated with the Senate Finance bill because they feel it doesn’t expand health insurance to enough people, and now they’re preparing to launch new advertisements citing the report’s findings of increased insurance premiums.

To discredit the report, Senate Finance Democrats turned to Thomas Barthold, chief of staff of the Joint Committee on Taxation, who took questions from the panel. Sen. Jeff Bingaman (D., N.M.) asked whether the insurance industry report, prepared by PricewaterhouseCoopers, overlooked several provisions in the bill that would lower insurance costs.